The present invention relates to a sodium-sulfur storage battery and a manufacturing method of the same, and more particularly, to a structure and a method for thermocompressively jointing an alpha alumina ring of ceramic to positive and negative covers of metal.
Conventionally, in a sodium-sulfur storage battery, an alpha alumina ring is jointed to negative and positive covers by means of thermocompressively jointing. This thermocompressively jointing is effective to joint the metallic material such as the negative and positive covers together with the different material such as the ceramic therebetween to electrically insulated the covers to each other, and is broadly utilized to form a perfectly sealed structure of a battery such as the sodium-sulfur storage battery which is operated at a high temperature. However, the negative and positive covers of the sodium-sulfur storage battery must have sufficient resistance to chemical and electrochemical attack by molten sulfur and sodium, and thus, are made from stainless steel. Therefore, in a heated condition before they are thermocompressively jointed, the surfaces thereof may be oxidized, resulting in insufficient gastightness. In order to prevent the oxidization, the thermocompressively jointing is performed in an atmosphere of insert gas or reducing gas or in the vacuum. However, these processes or methods require expensive equipment, and must be of batch type, which has low productivity.
Accordingly, it is an object of the invention to provide an improved sodium-sulfur storage battery and a manufacturing method, by which productivity is improved and gastightness by thermocompressively jointing is also improved.
According to the invention, negative and positive covers, which are made from stainless steel, iron or alloy of iron and nickel and are thermocompressively jointed to an alpha alumina ring, are provided on the surfaces with chrome diffusion layers and are provided at least on the surfaces, which are thermocompressively jointed, with coating layers of aluminium, and are thermocompressively jointed in the air to the alpha alumina ring.
The embodiments of the present invention is described by way of example, with reference to the accompanying drawings.